Although aluminum is ordinarily considered to be a bright metal, it often presents a dull or matte-like finish due to surface roughness resulting from the operations used to shape it, i.e., rolling, casting, extrusion and the like. For some applications, it is desired that aluminum have a highly-reflective surface. The term "highly reflective" is used herein to mean a surface which is glossy or polished and capable of reflecting a clear image.
Chemical and electrochemical solutions have been developed to create a highly-reflective surface on aluminum alloys and aluminum alloy bodies. These solutions are not entirely satisfactory. Chemical solutions do not create as high a quality surface as electrochemical solutions. Electrochemicals create a superior mirror-like surface; however, the process leaves a fine particulate material on the surface of the metal. This material is referred to as "smut".
The composition of the smut varies with the alloy and the electrochemical and chemical solution used to polish the surface but is generally composed of the oxides of the alloying metals. The smut is mostly aluminum oxide as well as those metallic compounds that do not dissolve during the polishing. The smut dulls the metal surface and detracts from the polished surface appearance. In addition, if it is not removed, subsequent deposits of chemical conversion coatings and the like will not be uniform and will be loosely held where the smut is not removed.
The electrochemical solutions leave a smut that is particularly difficult to remove without etching the surface. Chromated acid solutions have been found to be effective at removing smut caused by electrochemical solutions. However, these solutions must be used at temperatures above 160.degree. F. for them to be effective. In addition, chromated acid deoxidizing solutions are environmentally undesirable, and the Environmental Protection Agency (EPA) has enacted regulations which restrict chromium effluents. Consequently, in more and more finishing facilities, chromium treatment plants are being installed at great expense. Furthermore, restrictions on solid chromium disposal is also expensive.
Accordingly, it would be advantageous to provide a method for removing the smut from the surfaces of aluminum alloys possessing highly-reflective surfaces which does not destroy the high gloss on the surface of aluminum or diminish the ability of the surface to reflect a clear image.
Another object of the invention is to provide a chrome-free method for removing the smut from the surfaces of aluminum alloys possessing highly-reflective surfaces which does not destroy the high gloss on the surface of aluminum or aluminum alloy bodies.
Another object of the invention is to provide a chrome-free method for removing the smut from the surfaces of aluminum alloys possessing highly-reflective surfaces which is effective at room temperature.
Another object of the invention is to provide highly reflective sheet of aluminum alloys.
These and other objects and advantages of the present invention will be more fully understood and appreciated with reference to the following description.